Abstract

Radiation damage in Bi-2212 and (Bi0.92Pb0.17)-2212 superconducting pellets due to irradiation by 40 MeV He++-beam has been studied, as these two compounds differ with respect to lattice strain in their Bi-O and (Bi,Pb)-O layers. These samples were prepared with excess oxygen that accounts for their lowered superconducting transition temperature, Tc, of 59.5 and 64.5 K, respectively. Irradiation to 8.14×1015 He++/cm2raised Tcby 4.5 and 5.5 K, respectively, and also their normal state resistivities. Excess conductivity analysis for the unirradiated and irradiated samples showed (i) a transition of the conductivity fluctuation from 2D (λ=1.0) to 3D (λ=0.5) behaviour, on cooling across a temperature T0, and (ii) also the signature (λ=3.0) of critical fluctuations in a network of superconducting microregions, for temperatures below Tcr, where Tcr is seen to be 5 to 10 K lower than T0. The rise in Tchas been explained from irradiation-induced removal of oxygen taking the hole concentration towards the value for the peak in Tc.